The general goal of this work is to determine the kinetic mechanisms of sodium dependent amino acid transport in animal cells. This goal is important because sodium dependent systems are the principle means for accumulation and regulation of amino acids by cells yet little is understood about them. This project will focus on the kinetics of amino acid transport in internally dialyzed giant axons of Myxicola infundibulum and muscle fibers of the giant barnacle Balanus nubilus. The specific aims are: 1. Define influx and efflux as functions of the internal and external concentrations of sodium and amino acid. 2. Define the influx and efflux as functions of membrane potential. 3. Measure the sodium-amino acid flux coupling. Major emphasis will be placed upon the study of the transport of L-glutamic acid in muscle. Results will be important for basic understanding, and will enhance our knowledge of the regulation of glutamate in muscle where the compound plays a central role in cell homeostasis.